IGBT with channel resistors

ABSTRACT

An IGBT has striped cell with source stripes  2   a   , 2   b  continuous or segmented along the length of the base stripe  3.  The opposite stripes are periodically connected together by the N+ contact regions  20  to provide channel resistance along the width of the source stripes  2   a   , 2   b . For continuous stripes the resistance between two sequential contact areas  20   a   , 20   b  is greatest in the middle and current concentrates near the source contact regions  20.  The wider the spacing between the contacts  20,  the larger the resistive drop to the midpoint between two N+ contacts  20.

BACKGROUND

[0001] Insulated gate bipolar transistors (IGBTs) are popular controldevices for automobile ignition systems. The IGBT can carry largecurrents with very low resistance and can be rapidly switched on and offwith a low voltage gate. They combine the control characteristics ofDMOS devices with the current carrying capacity of thyristor.

[0002] A typical IGBT is shown in FIG. 4a. Those skilled in the artunderstand that some IGBTs are formed in striped cellular arrays ofbases with sources. As shown in FIG. 4a, the IGBT 10 has an epitaxiallayer 11 that includes two N+ source stripes regions 2 a, 2 b surroundedby P-typed base stripe regions 3. The portion 3 a of the base 3 thatlies between the source stripes is designated as the body stripe. Theepitaxial layer 11 has a lightly doped N drift region 5 over a heavilydoped N buffer region 7. The epitaxial layer 11 is formed on top of aheavily P doped substrate 9. On top of the device, gate insulatingstripes 17, typically of silicon dioxide, cover the top of the epitaxiallayer 11. Gate conductive stripes 19, typically polysilicon 19, coverthe insulating stripes 17 and form a gate electrode. The gate overlieschannel stripes 30 a, 30 b on opposite sides of the base stripe 3.Another insulating layer 21 covers the polysilicon stripes 19 and ametal contact stripe 23 contacts the source stripes 2 a, 2 b, N+ sourcecontact regions 20 and the body stripe 3 a of each cell. The abovedescription is for a planar device with the gate on the surface.However, the IGBT may be fabricated with a trench gate. See FIG. 4b.

[0003] IGBTs may be used in ignition control circuits such as thoseshown in FIGS. 1 and 2. Those circuits are discussed in this Backgroundportion of the specification in order to explain the invention. Thelocation of that discussion and the discussion itself are not admissionsthat the circuits are prior art. When the IGBT 10 is on, it drops a lowvoltage V_(CE(sat)) and current flows through the primary side 12 oftransformer 14. The ratio of the primary to the secondary coil 16 isabout 100:1. The voltage is allowed to build to about 400 volts acrossthe primary. When the spark plug is triggered, most of the energy isdischarged in the spark. If there is any residual energy, it isdissipated by an auxiliary clamp circuit 80. In FIG. 1 the clamp circuit80 a is a single pair or multiple pairs of Zener diodes 82, 84 with acumulative breakdown voltage of about 400 volts. In FIG. 2 the clampcircuit 80 b is a voltage divider including resistors R1, R2 and asingle pair or multiple pairs Zener diodes 86. After the gate signal isremoved, auxiliary circuits 80 keep the IGBT 10 on in order to dissipateresidual energy and prevent a localized failure.

[0004] The voltage for the auxiliary circuits 80 is set by the zenerdiodes to dissipate the energy over time. A problem arises if there isno spark due to, for example, a broken spark plug wire or a fouled plug.That leaves an open secondary 16 and the energy remains stored in theinductors 12, 16. With the gate turned off, the energy stored in theprimary 12 cannot be transferred to the secondary 16. The primary 12forces the voltage to rise until the zeners break down. In the selfclamped inductive switching (SCIS) mode a portion of the collectorcurrent, Izener, is diverted from the collector and into the gate tokeep the IGBT on. Then energy stored in the primary inductor 12 willdissipate even after the gate signal is removed.

[0005] In the SCIS mode the IGBT must absorb all the energy stored inthe ignition coil during abnormal operating conditions. The most commonabnormal condition is an open secondary. The silicon area of the IGBT isdefined by its SCIS energy density capability. Therefore, it isimperative that the SCIS energy density (mJ/cm²) be increased becauseshrinking the silicon area reduces cost and the IGBT footprint isreduced to free up module space. A 60% reduction in the footprint can berealized by offering the same SCIS capability in the DPak (TO-252)rather than a D2Pak (TO-263). Supplying the same device performance in aDPak allows the module designer to add this functionality withoutincreasing the module size.

[0006] In the clamping phase of the SCIS mode, a portion of thecollector current is fed back to the gate after the diodes in FIGS. 1and 2 avalanche. This current develops the required gate plateau voltageV_(GE(plateau)) across the R_(GE) or R₂ to deliver the necessary p-n-pbase electron current required to conduct the total decaying currentfrom the energy stored in the primary coil at the clamping voltage. SeeFIG. 3. The V_(GE(plateau)) continually self adjusts because it is afunction of the IGBT threshold voltage (V_(th)), p-n-p current gain(α_(p-n-p)), Pbase leakage current, and channel mobility (μ_(ns)). Allof the above are a function of the device temperature. SoV_(GE(plateau)) decreases with temperature because of the followingfactors:

[0007] 1. The V_(th) voltage has a negative temperature coefficient.

[0008] 2. The α_(p-n-p) has a positive temperature coefficient, reducingthe percentage of electron current to deliver the total decaying SCIScurrent.

[0009] 3. The electron current generated from the Pbase leakage currenthas a positive temperature coefficient. Refer to stripe cellcross-section shown in FIG. 4. This reduces the amount of electroncurrent required to drift across the channel because the leakage currentcan supply part of the p-n-p base current.

[0010] V_(GE(plateau)) increases with temperature because thedegradation in μ_(ns) with increasing temperature causes a de-biasingeffect.

[0011] Factors 1, 2, and 3 outweigh factor 4. So as the device 10 heatsup and current decays V_(GE (plateau)) will decrease at an acceleratedrate. If V_(GE (plateau)) reaches zero anywhere on the die while thetemperature is still rising and an appreciable amount of current (>1A)is still decaying from the primary to induce localized thermal runaway,the device will fail to maintain the clamping function and may faildestructively. As such, it is desirable to find a solution for keepingV_(GE(plateau)) high during SCIS clamping.

[0012] Others have tried to extend the SCIS capability by decreasing thecell pitch to more uniformly distribute the heating during SCIS byreducing the localized current density. In some designs the cell is fullchannel and N+ channel doping is contacted along the entire length ofthe stripe as showed in FIG. 5. With such designs, V_(GE) (plateau)during SCIS is reduced because the electron current density per unitchannel width is reduced. Thus, such designs fail to improve SCISperformance. Another design to improve SCIS performance relies upondividing the channel width into multiple segments as shown in FIG. 6.The channel width is reduced by excluding the N+ channel doping. Thiscan be accomplished by a simple lithographic bar pattern with theresults shown in the bottom half of FIG. 6. The N+ doping need not becontinuous across the contact opening as shown in the top half of FIG.6. The segments of the channel can be connected in their centers or attheir ends. See the versions showed in FIGS. 7 and 8. In both figures,contact is made again along the full length of the N+ channel doping.The N+ contact areas are not required, nor must they be continuousacross the contact opening. These methods increase V_(GE(plateau)) andthe electron current density per unit channel width. The higher electroncurrent per unit channel width increases the maximum peak temperaturebefore all the IGBT p-n-p base current can be supplied by the increasingPbase leakage current.

SUMMARY

[0013] The invention improves SCIS performance by altering the structureof the source contact regions and by altering the structure of thesources. In particular, channel resistances are added to the device inorder to more effectively distribute the heat across the surface of thedie. The construction of the IGBT is altered so that contact to thesource stripes is made only substantially through the source contactregions. As such, prior art techniques that relied upon contacting thesource stripes along their entire length are not used. The portion ofthe source stripe adjacent the body region is either excluded fromdoping or is suitably shielded by an insulating layer. The inventionalso divides source stripes along the width of the channel into aplurality of segments. These segments may be of equal length andopposite each other and connected at their middles by a source contactregion. In another embodiment the source stripe segments may be joggedwith respect to each other so that the source contact region connectsthe head of one segment to the tail of another segment on the oppositeside of the body stripe.

[0014] The invention provides an insulated bipolar transistor device(IGBT) that has a substrate heavily doped with a first dopant of onepolarity, conventionally P-type doping. Above the substrate are bufferand drift layers typically comprising N-type dopants. The buffer layeris heavily doped and adjacent the substrate. The drift layer is morelightly doped and extends to the surface of the device. The surface ofthe device has a number of elongated base stripe regions formed withP-type dopants. Each base stripe region is bordered by the drift layerand extends along a length of the surface. The IGBT has numerous basestripes. Within each of the base stripes there are first and secondsource stripes. The source stripes are typically formed with N-typedopants and are located opposite each other and near the edges of theirbase stripe. The source stripes are essentially parallel to each otherand extend in the same direction as the base stripes. A region in thebase stripe and between the source stripes define a body stripe ofP-type dopant. Portions of the base stripe between the source stripesand the proximate bordering drift layer define channel regions for theIGBT. A gate electrode is over each channel. The gate electrodes includegate oxide stripe, a conductive gate stripe and an insulating layer overthe conductive gate stripe. A source contact layer, typically of metal,extends through vias in the insulating layer. The vias are at a numberof locations aligned with the polysilicon gate and body stripe. Thesource contact layer fills the vias in the insulating layer and makescontact to a number of source contact regions. The source contactregions are typically heavily N-doped and are disposed in the bodystripe. The source contact regions extend from the body stripe to one orboth of the source stripes and are in electrical contact with the sourcecontact layer. The insulating layer covers the portions of the sourcestripes that are proximate the body regions. Thus, the only contact tothe source stripes is through the source contact regions.

[0015] In one embodiment, the source stripes are continuous and areperiodically interconnected by source contact regions. The sourcecontact regions and the source stripes may have the same heavy N-typedoping. As an alternative, their stripes may have less of an N-typedoping concentration. The invention also divides the source stripes intoa plurality of elongated source segments comprising head and tailsections and elongated bodies. The source segments are spaced from eachother along opposite sides of the body stripe. Portions of the bodyregion extend between sequential head and tail sections of the segmentsin order to separate the sequential source stripe segments from eachother. In one embodiment the source segments are the same length and areconnected together at approximately the middle of their lengths by ansource contact region. In another embodiment, the source stripes oneither side of the body region are jogged with respect to each other. Inthat embodiment, the head of a source stripe on one side of the bodystripe is connected across the body to the tail of another source stripeon the opposite side of the body stripe by a source contact region.

DRAWINGS

[0016]FIGS. 1 and 2 are circuit diagrams of IGBT driver circuits forautomobile ignitions.

[0017]FIG. 3 is a graphic representation of operation of the IGBT beforeand during SCIS mode.

[0018]FIGS. 4a, 4 b show conventional surface gate and trench gateIGBTs.

[0019]FIGS. 4c, 4 d show expanded partial cross section and perspectiveviews of a conventional surface gate IGBT.

[0020]FIG. 5 is a detailed expanded plan view of a conventional IGBTstripe cell.

[0021]FIG. 6 is a detailed expanded plan view of a conventional IGBTwith source excluded sections.

[0022]FIG. 7 is a detailed expanded plan view of an IGBT stripe cellwith source segments connected at their middles.

[0023]FIG. 8 is a detailed expanded plan view of an IGBT stripe cellwith source segments connected head to tail.

[0024]FIG. 9 is a detailed expanded plan view of an IGBT with channelresistances.

[0025]FIG. 10 is a set of graphs comparing selected characteristics ofthe performance of a device made in accordance with FIG. 5 to those of adevice made in accordance with FIG. 14.

[0026]FIG. 11 is another set of graphs comparing Pbase temperature andvoltage characteristics of devices made in accordance with FIGS. 5 and9.

[0027]FIG. 12 is a graph comparing the SCIS energy of a device made inaccordance with FIGS. 5 and 14.

[0028]FIG. 13 is a detailed expanded plan view of an IGBT stripe cellwith channel resistances and source segments connected at their middles.

[0029]FIG. 14 is a detailed expanded plan view of an IGBT stripe cellwith channel resistances and source segments connected head to tail.

[0030]FIG. 15 is a partial expanded plan view of the invention in atrench gated IGBT with channel resistors along the width of the gate.

[0031]FIG. 16 is a partial expanded plan view of the invention in atrench gated IGBT with segmented sources contacted at their middles.

[0032]FIG. 17 is a partial expanded plan view of the invention in atrench gated IGBT with segmented sources contacted at their respectiveheads and tails.

DETAILED DESCRIPTION

[0033] Details of the structure of typical prior art devices are shownin FIGS. 4c and 4 d. Those figures show two source stripes 2 a, 2 bwithin base strip 3. The gate electrodes 19 a, 19 b overly portions ofthe gate stripes to 2 a, 2 b and outer portions of the base stripe 3.The electrodes 19 a, 19 b induce channels 30 a, 30 b between the outeredges of the source stripes 2 a, 2 b and the drift layer 5. Dielectricstripes 21 a, 21 b enclose the upper portions of the gates 19 a, 19 band have vias 40 for source contact metal. In a conventional IGBT thesource contact metal 40 makes electrical and mechanical contact withsource contact diffusion regions 20 a, 20 b, . . . 20 n as well asinside portions of the source strips 2 a, 2 b. Note that the insideportions designated 41 a, 41 b are contacted by the source metal 23.

[0034]FIG. 5 is a detailed plan of a portion of a stripe cell in thestructure as illustrated in FIGS. 4a, 4 c and 4 d. The central portionshows two channel stripes 2 a, 2 b in base stripe 3 that are separatedby portion 3 a of the base stripe. N+ contact regions 20 a, 20 b, 20 care shown. Likewise, the source metal contacted regions 41 a, 41 b ofthe source stripes 2 a, 2 b are also shown. The source metal makescontact with the exposed portions of the N+ contact regions 20 and theportions 41 a, 41 b of the stripes 2 a, 2 b. Thus, the entire width ofthe channel is contacted by the source metal. That structure does notimprove SCIS performance.

[0035]FIG. 6 shows one attempt to improve performance of the IGBT bydividing the source stripes into numerous source contact regions 20.Some of these regions extend across most of the base 3 to providechannel regions. See for example source contact regions 20 a-20 d. Othersource contact regions such as 20 el and 20 er are spaced on oppositesides of the base stripe. It is not necessary that the source contactregions 20 be continuous across the base stripe 3. The structure shownin FIG. 6 is formed by providing a suitable mask that will exclude N+source regions from undesired areas and leave only the Pbase 3 in thoseareas.

[0036]FIGS. 7 and 8 show further examples of speculative structures thatcan be made with prior art techniques. No admission is made in thisapplication that FIGS. 7 and 8 are, per se, prior art. One could dividethe gate stripe 2 into a plurality of segments such as 2 a.1 that isopposite segment 2 b.1 and segment 2 a.2 that is opposite segment 2 b.2. . . 2 a.n opposite 2 b.n. Each of the pairs of segments 2 an., 2 b.nare connected near the middle of their length by a heavily doped N+contact 20. As such, N+ contact 20 b connects source segments 2 a.2 and2 b.2. The regions 30 a, 30 b, . . . 30 n between the heads (H) and thetails (T) of the sequential source segments are P-doped as is the Pbase.A jogged or z-type structure is shown in FIG. 8. There, the head of astriped segment on one side is connected to the tail of the nextsequential source stripe on the opposite side of the base 3. So, thehead of source stripe segment 2 a.1 is connected via N+ contact region20 b to the tail of source stripe segment 2 b.2.

[0037] The invention overcomes the problems of the prior art byisolating the source stripes from the source metal contact to increasethe resistance of the channel along the width of the channel. In theembodiment shown in FIG. 9, these results are achieved by narrowing thesource stripes 2 a, 2 b or extending the dielectric 21 a, 21 b so thatthe source stripes are entirely disposed beneath the dielectric layers21 a, 21 b and are not contacted by the source metal 23. As such, theonly contact to the source stripes 2 a, 2 b is through the periodicsource contact regions 20. The stripes 2 a, 2 b remain continuous alongthe length of the base stripe 3. The source stripes on opposite sides ofbase stripe 3 are periodically connected together by N+ contact regions20. That structure provides channel resistance along the width of thesource stripes 2 a, 2 b. The resistance between two sequential contactareas 20 a, 20 b is greatest in the middle. As such, the channelresistors concentrate current near the source contact regions 20. Thewider the spacing between the contacts 20, the larger the resistive dropto the midpoint between two N+ contacts 20 and the higher the N+ sourcecontact resistance due to reduced contact area. The N+ contacts can becontinuous across the contact opening or extend partially across asshown in the top portion of FIG. 6. The channel resistors function tolocally offset decreases in V_(GE) (plateau) by constricting the flow ofthe electron current to smaller areas as the temperature increases dueto the positive temperature coefficient of the resistor. While thelarger spacings (50 um or greater) between N+ contacts further offsetthe decrease in V_(GE) (plateau) due to the increased contactresistance. When temperature rises in a certain area of the die due toSCIS induced self-heating, the voltage drop down the length of the localresistor and at the N+ contacts increases. The highest voltage drop isfurthest from the N+ contact. Thus, a gradual de-biasing of the gateoccurs along the channel resistor to the N+ contact. At roomtemperature, the de-biasing effect is small. An electron current flowsthrough the channel almost uniformly down the length of the resistor.However, as the temperature increases and the current continues todecay, the conduction of the electron current through the channel startsto constrict along the entire channel resistor length to smaller areasdirectly across from the N+ contacts 20. This effectively reduces thechannel width of the IGBT. The reduction in effective channel width ofthe IGBT forces the gate to maintain a higher bias to pass the totalcurrent. The effect of this structure is demonstrated in FIG. 10.

[0038] There the V_(GE) (plateau) of the full channel design (FIG. 5)decays linearly. However, the V_(GE) (plateau) is higher for the channelresistor design and has a nonlinear decay because the electron currentis constricted as the temperature increases. The constriction ofelectron current into these smaller areas increases the maximum peaktemperature before all the IGBT p-n-p base current can be supplied bythe increasing Pbase leakage current. When this occurs, the IGBT gatecontrol is lost, thermal runaway occurs, and the clamping functionfails. This is demonstrated by the simulated wave forms in FIG. 11.Although the increase in channel resistance due to the temperatureeffect was not modeled, the simulations show that the device must reach30° C. to 40° C. higher peak Pbase temperature for the clamping functionto fail on the device with the channel resistance invention compared tothe full channel device of FIG. 5. The temperature difference would behigher with the channel resistance temperature affect included. Themeasured comparison in SCIS energy density improvement as a function ofstarting junction temperature at the initiation of the SCIS mode isshown in FIG. 12. There it can be seen that the SCIS energy density isuniformly higher for the channel resistor as compared to the fullchannel for all temperatures.

[0039] The invention can also be applied to segmented source structures.Examples of the invention of such structures are shown in FIGS. 13 and14. FIG. 13 has the source segments 2 a and 2 b disposed on oppositesides of the base stripe 3 and separated by the body 3 a. Note: that thecontact opening is sized with the narrower source stripes 2 a, 2 b sothat only the source contact regions 20 are available for contact. Theheads and tails of sequential sources are separated by the Pbase region3.

[0040]FIG. 14 adapts a z-shaped structure to the invention. There thesource stripes 2 a are jogged with respect to the source stripes 2 b. Assuch, the head of one source stripe 2 a.1 terminates at about a locationwhere an opposite, jogged source stripe tail of 2 b.2 begins. The sourcestripes are connected by N+ contacts 20 a.1, 20 a.2. As mentioned above,the contact may be continuous or may be interrupted. Either structure issuitable for the invention.

[0041] Having thus described the invention and several embodimentsthereof, those skilled in the art will appreciate that furthermodifications, additions and omissions of elements may be made to theinvention without departing from the spirit and structure as set forthin the claims. In particular, the invention can be adapted to trenchgated IGBTs such as the samples shown in FIG. 4b. Turning to FIG. 15,the invention is showed in a trench gated IGBT. The gate polysilicon 19is in the middle. Source stripes 2 a, 2 b and base stripes 300 a, 300 bare separated by the gate oxide 17 that cover the walls of the trench.The insulating layer 21 extends over the gate, over the source stripes 2a, 2 b and over a portion of the base stripes 300 a, 300 b. Sourcecontact regions 20 nl and 20 nr contact the source stripes 2 a, 2 b onopposite sides of the gate trench. Channel resistances CR are formed inthe portions of the source stripes between the contact regions. Thisembodiment of the invention is similar to the planar gate embodimentshown in FIG. 9. FIGS. 16 and 17 show other trench gate embodiments thatare similar respectively to the planar embodiments showed in FIGS. 13and 14, respectively. In FIG. 16 selected portions of the source stripeare excluded to form source segments of equal length. The segments onopposite sides of the trench are contacted. In FIG. 17 source segmentsare jogged with respect to each other. Segments on opposite sides of thetrench have source contacts at opposite heads and tails.

[0042] Those skilled in the art will understand that the invention maybe embodied in other configurations. For example, the lengths of thechannel resistors may be different depending upon their location. Ingeneral, shorter lengths closer to the center of the die are preferred.In addition opposing segments of the embodiment shown in FIGS. 13, 14and 15, 16 do not have to be the same length. Similar results can beachieved by masking and doping the source stripes and source segments toalter the resistance of the channel resistors. Those skilled in the artalso understand that the base stripes may be connected together at theirends to form a common base for the device.

1. An insulated gate bipolar transistor device (IGBT) comprising: asubstrate heavily doped with a first dopant of one polarity; buffer anddrift layers doped with a second dopant of a polarity opposite to thefirst dopant, the buffer and drift layers located over the substrate,with the drift layer extending to a surface opposite the substrate; aplurality of base regions doped with the first dopant, each base regionbordered by the drift layer, and each base region extending along thelength of the surface to form a plurality of base stripes on the onesurface of the device; first and second source stripes doped with thesecond dopant and located in each base stripe, the source stripes beingparallel to each other and extending in the same direction as the basestripes, the source stripes spaced from each other to define a bodystripe between the source stripes and spaced from edges of the basestripe to define first and second channel regions extending in oppositedirections across opposite edges of the base stripes from each of thesource stripes to the nearest border of the drift layer; a gate oxidestripe over the channels on the surface and a conductive gate stripe onthe gate oxide stripe for controlling current through the channels; aninsulating layer over the conductive gate stripes and covering the edgesof the source stripes proximate the body stripe; a source contact layerextending through the insulating layer at a location between oppositegate stripes; a plurality of source contact regions heavily doped withthe second dopant, disposed in the body stripe and extending from thebody stripe to at least one of the source stripes and in electricalcontact with the source contact layer.
 2. The IGBT of claim 1 whereinone or more source contact regions extend from the body stripe inopposite directions to each source stripe.
 3. The IGBT of claim 1wherein the source stripes are continuous along the length of the bodystripe.
 4. The IGBT of claim 1 wherein the source stripes are dividedinto a plurality of elongated source segments spaced from each otheralong opposite sides of the body stripe, and portions of the body regionextending between opposite ends of sequential segments to separate thesequential source stripe segments from each other.
 5. The IGBT of claim1 wherein the base stripes are connected together to form a common base.6. The IGBT of claim 4 wherein the source contacts extend from onesource segment across the body stripe to the opposite source segment. 7.The IGBT of claim 6 wherein the source contacts extend from the middleof one source segment to the middle of the opposite source segments. 8.The IGBT of claim 4 wherein the source segments are the same length. 9.The IGBT of claim 4 wherein source stripes have forward and rearwardends and the ends of stripes on opposite sides of the body stripe aredirectly opposite to each other.
 10. The IGBT of claim 4 wherein sourcestripes have forward and rearward ends and the ends of stripes onopposite sides of the body stripe are jogged with respect to each other.11. The IGBT of claim 4 wherein the source segments are the same length.12. The IGBT of claim 4 wherein the source segments are of differentlengths.
 13. The IGBT of claim 11 wherein the length of the sourcesegment depends upon its proximity to the center of the IGBT.
 14. TheIGBT of claim 13 wherein the length of the source segment depends upon adesired local SCIS current density.
 15. The IGBT of claim 1 wherein theedges of the source stripes adjacent the body stripe are electricallyisolated from contact with the source contact layer.
 16. The IGBT ofclaim 1 wherein doping concentration in the source stripes is the sameas the doping concentration in the source contact regions.
 17. The IGBTof claim 1 wherein doping concentration in the source stripes is theless than the doping concentration in the source contact regions. 18.The IGBT of claim 1 wherein the first dopant is p-type and the seconddopant is n-type.
 19. The IGBT of claim 1 wherein the first dopant isn-type and the second dopant is p-type.
 20. An insulated gate bipolartransistor device (IGBT) comprising: a substrate heavily doped with afirst dopant of one polarity; a drift layer over the substrate and dopedwith a second dopant of an opposite polarity, the drift layer extendingto a surface opposite the substrate; base regions doped with the firstdopant, each base region bordered by the drift layer and each baseregion extending along a length of the surface to form a plurality ofbase stripes on the surface of the device; source stripes with seconddopants in the base regions proximate the border of the base regions toform channel regions extending from the source stripes to the proximateborder of the drift layer and the base stripe; an insulated control gateover the base regions, between the source stripe and the drift layer andover the channel regions; source contact regions disposed adjacent thesource stripes; resistances disposed between the source contact regionsand the source stripes for constricting the flow of electron currentbetween the drift layer and the source contact regions.
 21. The IGBT ofclaim 20 wherein the source contact regions are spaced from each otheralong the length of the source stripes to connect opposite stripes toeach other only at spaced apart locations and thereby provide theresistances.
 22. The IGBT of claim 20 wherein the base regions areconnected together to form a common base.
 23. The IGBT of claim 20wherein the source stripes are sequentially segmented and sequentialsegments are separated from each other by the base region.
 24. The IGBTof claim 23 wherein source segments opposite each other are the samelength and are connected at their respective middles by an sourcecontact region.
 25. The IGBT of claim 23 wherein the sequential segmentsof opposite source stripes are jogged with respect to each other and areconnected together at their opposite, jogged ends by an source contactregion.
 26. The IGBT of claim 20 wherein the first dopant is p-type andthe second dopant is n-type.
 27. The IGBT of claim 20 wherein the firstdopant is n-type and the second dopant is p-type.
 28. An insulated gatebipolar transistor device (IGBT) comprising: a substrate heavily dopedwith a first dopant of one polarity; a drift layer over the substrateand doped with a second dopant of an opposite polarity, the drift layerextending to a surface opposite the substrate; a trench gate in thesurface of the drift layer including a gate insulator on the insidesurface of the trench and a conductive material adjacent the gateinsulator forming the gate electrode; base regions doped with the firstdopant, each base region divided by the gate trench, bordered by thedrift layer and extending along a length of the surface to form aplurality of base stripes on the surface of the device; source stripesregions disposed between the base stripes and the trench and shallowerthan the base for forming channel regions along the outside surface ofthe trench; source contact regions extending between the base regionsand the source stripes; a plurality of channel resistances in the sourcestripes and disposed between the source contact regions;
 29. The IGBT ofclaim 28 further comprising: a insulating layer over the trench gate andover source stripe regions; a plurality of vias in the insulating layerand over the source contact regions; a source contact layer over theinsulating layer and extending through the vias therein to contact thesource contact regions in the source stripes.
 30. The IGBT of claim 28wherein the source contact regions are spaced from each other along thelength of the source stripes to connect the source contact layer to thesource stripes only at spaced apart locations and thereby provide thechannel resistances.
 31. The IGBT of claim 26 wherein the base regionsare connected together to form a common base.
 32. The IGBT of claim 30wherein the source stripes are sequentially segmented and sequentialsegments are separated from each other by the base region.
 33. The IGBTof claim 32 wherein source segments opposite each have source contactregions in the middle of the segments.
 34. The IGBT of claim 30 whereinthe sequential segments of opposite source stripes are jogged withrespect to each other and sequential segments on one side of the trenchhave source contact regions at the heads of the segments and sequentialsegments on the other side of the trench have source contact regions atthe tails of the segments and the heads of the one segments are oppositethe tails of the other segments.
 35. An insulated gate bipolartransistor device (IGBT) comprising: a substrate heavily doped with afirst dopant of one polarity; a drift layer over the substrate and dopedwith a second dopant of an opposite polarity, the drift layer extendingto a surface opposite the substrate; base regions doped with the firstdopant, each base bordered by the drift layer and extending along alength of the surface to form a plurality of base stripes on the surfaceof the device; two source stripes regions disposed inside each basestripe, the source stripe regions shallower than the base for formingchannel regions at a junction of the base stripe and the source stripe;source contact regions extending between the base regions and the sourcestripes; an insulating layer covering the source stripes and having viasabove the source contact regions; a source contact layer over the sourcestripes and in the vias for contacting the source contact regions. aplurality of channel resistances in the source stripes and disposedbetween the source contact regions; a gate including a gate insulatorand conductive material adjacent the gate insulator forming the gateelectrode, said gate disposed over the channel region formed by the baseand source stripes.
 36. The IGBT of claim 35 wherein the source contactregions are spaced from each other along the length of the sourcestripes to connect the source contact layer to the source stripes onlyat spaced apart locations and thereby provide the channel resistances.37. The IGBT of claim 35 wherein the source stripes are sequentiallysegmented and sequential segments are separated from each other by thebase region.
 38. The IGBT of claim 35 wherein the base regions areconnected together to form a common base.
 39. The IGBT of claim 37wherein source segments opposite each have source contact regions in themiddle of the segments.
 40. The IGBT of claim 34 wherein the sequentialsegments of opposite source stripes are jogged with respect to eachother and sequential segments on one side of the trench have sourcecontact regions at the heads of the segments and sequential segments onthe other side of the trench have source contact regions at the tails ofthe segments and the heads of the one segments are opposite the tails ofthe other segments.
 41. The IGBT of claim 32 wherein the gate is aplanar gate on the surface of the IGBT over the base region.
 42. TheIGBT of claim 32 wherein the gate is a trench gate extending from thesurface into the base region.